The invention relates to a mobile and exclusively manually actuated strapping unit according to the preamble of claim 1.
Strapping units of this type are provided for mobile use so that a user can wrap a steel strap around a packaged item in any desired location. This type of strapping unit typically has a sealing device which produces a connection of two layers of the steel strap by means of multiple notchings, without using an additional sealing element, such as, for example a lead seal. For this type of strapping unit it is also typical for both the strap tension and the formation of a seal to be produced manually without the assistance of outside energy, in particular electric or hydraulic energy. For this purpose, the operator of a strapping unit according to the generic type has only to provide his own muscular power.
However, this entails a number of concept-induced problems, for example that a sufficiently large force can be provided in order to form the seal. In order to be able to apply as large a force as possible, particularly right at the beginning of the contact of the die-plate, which is arranged in the die-plate carrier, with the steel strap, the die-plate carrier is mounted pivotably. By this means, initially only a relatively small surface of the die-plate comes into contact with the steel strap. The high surface pressure caused as a result is intended to ensure that the metal strap is sufficiently deformed from the beginning.
A strapping unit of this type is shown, for example, in U.S. Pat. No. 4,398,572. In this case, however, it is disadvantageous that there is a concentration of mass in the region over the front end of the base plate of the strapping unit. This distribution of weight results in a xe2x80x9ctop-heavinessxe2x80x9d which makes the handling of the unit more difficult.
The invention is therefore based on the object of providing a unit of the type mentioned at the beginning with improved handleability.
This object is achieved according to the invention in the case of a strapping unit according to the preamble of claim 1 according to a first aspect in that at least in the sealing end position of the sealing-device lever a contact region of the transmission element with the die-plate carrier is arranged, with respect to a direction running parallel to the orientation of the strap between the sealing device and the tensioning wheel, approximately level with the separating means or behind the separating means. This is synonymous with shifting the contact region (and therefore preferably also the bearing point of the sealing-device lever on the strapping unit) toward the tensioning device. This enables, in an advantageous manner, a more balanced distribution of weight to be obtained than is the case with the unit described in U.S. Pat. No. 4,398,572. In the case of the unit from U.S. Pat. No. 4,398,572, its transmission element, therefore also the rotational shaft of the sealing-device lever, is arranged upstream of the notching tool in the tensioning direction, which causes the concentration of mass, which is to be avoided by the invention, in the region of the top-end rotational bearing of the unit.
In addition, this solution affords the advantage that a lever arm, with which the transmission element, with respect to the bearing point of the die-plate carrier on the strapping unit, presses onto the die-plate carrier, is extended. This enables a relatively large torque to be produced with respect to the bearing point of the die-plate carrier, as a result of which a sufficiently large force for deforming the strap can be ensured in a very reliable manner, particularly at the beginning of the sealing process.
However, considerable advantages can also be obtained with the device according to the invention if, in comparison to previously known strapping units, it is not required to increase the torque acting on the die-plate carrier. A relatively long lever arm, which can be obtained according to the invention, between the bearing point of the die-plate carrier and the contact region of the transmission element with the die-plate carrier enables the forces acting in order to produce a seal to be reduced. These are the forces which, starting from the die-plate carrier, act between a bearing surface for the steel strap on the upper side of the base plate and the bearing point for the sealing-device lever. This means, in an advantageous manner, that those components of the strapping unit which are provided here, can be of less solid dimensions than hitherto. This also results in a reduction in weight in the front region of the strapping unit and therefore improves the handleability of the unit.
According to a further aspect, the object in the case of a strapping unit as described in the preamble of claim 1 and in which the tensioning wheel is mounted on a pivotable rocker is also achieved in that a bearing axis of the rocker and a rotational axis of the sealing-device lever are at least substantially aligned with each other. This also signifies, with respect to a horizontal direction of the strapping unit along the base plate, a shifting of the rocker axis in the direction of the rear end of the base plate toward the tensioning wheel and results in an advantageous distribution of weight. This solution even affords the further advantage that because two previously separated bearing points are consolidated, a reduction in the number of required individual parts can be obtained. A particularly favorable solution in terms of structure can be provided here by the rocker and the transmission element being arranged on the same shaft. The reduction in the required individual parts concerns, in particular, components which, in the case of previously known strapping units according to the generic type, are situated above the front half of the base plate and therefore contribute to the top-heaviness.
In an advantageous embodiment, provision can be made according to the invention that during a transfer of the die-plate carrier from its open end position into the sealing end-position, the point at which the transmission element is in contact with the die-plate carrier migrates in order to transmit the movement of the sealing-device lever to the die-plate carrier. The contact region preferably changes in such a manner that the normal force vector of the transmitted force encloses, together with an orthogonal of the supporting surface of the base plate, at an angle which increases toward the sealing end position during a pivoting movement of the sealing-device lever. This firstly enables the lever arm to be further increased and secondly enables the force profile at the free end of the sealing-device lever to be improved.
Further preferred embodiment of the invention emerge from the dependent claims, the description and the drawing.